This invention relates generally to hard disk drives. More particularly, it relates to hard disk drives containing volatile organic compounds for corrosion protection.
Current growth rates for the digital magnetic recording data storage industry show an increase in recording densities of 60% per year. To continue at this growth rate, the recording industry is being forced to make a number of significant changes in the design of the magnetic recording devices. Digital magnetic recording devices, typically referred to as xe2x80x9chardxe2x80x9d disk drives, for data storage generally include a thin film magnetic recording disk and a head or transducer which is moved along or above the surface of the rotating disk to read and write information on the disk. The decreasing bit cell size associated with increasing data and areal density requires increasing coercivity of the magnetic recording film to avoid thermal demagnetization and a smaller physical spacing between the head and the magnetic layer of the disk.
To accommodate these requirements, the magnetic materials in the head and the recording disk must be modified. The magnetic recording film on the disk typically contains Co and Cr. The magnetic recording head elements typically contain Nixe2x80x94Fe alloy (permalloy), Ta, Cu, and Co. A giant magnetoresistive (GMR) or magnetic tunnel junction (MTJ) and inductive write head may contain materials such as Co, Cu, Ru, Ni Oxide, or XMn, where X can be Pt, Ni, or Ir. High moment write heads may contain alloys of Co, Fe and Ni. These metallic head and disk materials are susceptible to corrosion during storage or in use environments. The chemically reactive metals in current products are protected from corrosion by approximately 1-10 nm thick carbon overcoats. The overcoat thickness is continuously being reduced, or eventually to be eliminated, to decrease the physical spacing between head and disk, and to increase the areal recording density. In the absence of thin impermeable overcoats, water and other corrosive vapors are able to penetrate through pinholes of the porous carbon and any oxide layers on the reactive metal films and corrode the parts, thus rendering the disk and head element non-functional and unreliable.
The corrosion of unprotected metal films is determined by the composition of the vapor phase within the enclosure of the disk drive. Vapor phase composition can be controlled by a desiccant to maintain low humidity, adsorptive chemical filters to eliminate hydrocarbons and corrosive vapors (U.S. Pat. No. 5,229,899), and stringent quality control on the cleanliness and out-gassing of internal components through vacuum post-baking. Advanced material selection, vacuum post baking, and adsorptive chemical filters have practically eliminated uncontrolled vapor phase components in disk drives. However, even though the drive interior is extremely clean and dry, corrosion of sensitive reactive metal parts of the head and recording disk is still possible during exposure to harsh environmental conditions. For example, a TEM cross-section of a GMR head after 100 hours exposure at 120xc2x0 C. and 93% relative humidity (RH) showed the disappearance of Co and Cu throughout the 0.5 micron thick stripe.
Japanese patent number JP58048278, issued to Yanagisawa on Mar. 22, 1983, discloses a magnetic recording device including a volatile corrosion inhibitor placed in a container for preventing corrosion of the magnetic disks. However, the volatile anti-corrosion agents, which includes iso-, di-, or triamine, their nitrites, benzoates, and carbonates, used in the Yanagisawa magnetic recording device are not effective in corrosion protection for metal alloys of the head and disk in current products.
U.S. Pat. No. 5,909,337, issued to Tyndall on Jun. 1, 1999, discloses a magnetic recording device having a liquid or solid volatile base for preventing the polymerization of gaseous contaminants at the head-disk interface. However, the volatile base of Tyndall cannot prevent the corrosion on the disk and head surface.
U.S. Pat. No. 5,023,738, issued to Prenosil on Jun. 11, 1991, discloses a magnetic recording head coated with a silane, zirconate or titanate compound to prevent atmospheric corrosion. However, Prenosil does not teach the protection of magnetic surfaces of recording disks of the hard disk drives from corrosion. These protective coatings are not applicable for coatings less than 2 nm thick required on future magnetic recording heads.
There is a need, therefore, for an improved magnetic recording device in which the magnetic surfaces of the recording disk and the GMR or MTJ and inductive write head are protected from corrosion.
A hard disk drive (HDD) with a vapor phase corrosion inhibitor (VPCI) package for providing molecular level corrosion protection of the giant magnetoresistive (GMR) or magnetic tunnel junction (MTJ) and inductive write head and recording disk surfaces is described in an exemplary embodiment of the present invention. A hard disk drive typically includes a magnetic recording disk and a GMR or MTJ and inductive write head supported on a slider for magnetically reading or writing data from or to the magnetic recording disk. The slider is connected to an actuator for moving the head across the magnetic recording disk, which is moved relative to the head by a mechanism such as a motor. The disk drive is sealed in a housing with a VPCI package attached to an interior surface of the housing.
The VPCI package includes vapor phase corrosion inhibitor (VPCI) material embedded or dissolved in a polymeric matrix with the weight of the VPCI material in the range of 0.1% to 20% of the weight of the polymeric matrix. The polymeric matrix can be a thermoplastic polymeric matrix or an elastomer matrix. The VPCI package can be held inside the disk drive in many other ways, including deposited on a fibrous carrier or contained in a pouch with pinholes or labyrinth channels, for controlled release. The VPCI material is selected so as not to degrade the mechanical performance of the disk drive, and so as not to form particles inside the disk drive.
The VPCI material typically includes either one or a combination of a benzotriazole, a salt of a primary or secondary organic amine in combination with an organic acid, and an amine salt in combination with an inorganic acid. Specifically, the VPCI includes either one or a combination of 5-methyl benzotriazole, benzotriazole, butylated hydroxy toluene, di-tert-butyl benzoquinone, octafluoro hexanediol, and dicyclohexylammonium benzoate.
The components of the VPCI have sufficient vapor pressures to provide finite concentrations in the vapor phase and adsorbed films on the exposed surfaces of the magnetoresistive or magnetic tunnel junction and inductive write head and the recording disk. The vapor pressure is typically within 10xe2x88x924 Pa to 103 Pa between 20xc2x0 C. and 100xc2x0 C. Therefore, the vapor phase concentration of the VPCI components are selected to provide a predetermined adsorbed film thickness, which is typically between 0.1 nm and 5 nm. The maximum thickness of the adsorbed film is selected so as not to interfere with the physical spacing of the head flying over the disk.
The rate of the VPCI transferring from the VPCI package into the disk drive enclosure is controlled over the lifetime of the drive. The partial pressure of VPCI in the enclosure depends on the VPCI source term (the evaporation rate of the VPCI from the polymeric matrix), and the VPCI sink term (leaks and absorbers). The net VPCI evaporation rate, per unit area, of the VPCI package within the enclosure depends upon the solubility and diffusivity of the VPCI material in the polymeric matrix and the partial pressure of VPCI in the enclosure. Varying the area, composition, and thickness of the polymeric matrix can control the maximum evaporation rate of the VPCI from the VPCI package. These characteristics of the polymeric matrix can be controlled by altering the monomer, polymer chain length, crosslinking or melt processing of the polymeric matrix. The polymeric matrix can be made of polyolefin, such as polyethylene, polyurethane, polyamides, polyethers, and polyesters, or vinyl type polymers.
In a preferred embodiment, polyethylene is used to make the polymeric matrix. Polyethylene is a highly variable material, ranging from soft, highly branched, low density to stiff, linear, high density. Polyethylene can be extruded in thicknesses from 0.1 mm to 1 mm and can be co-extruded so that a film is produced with a stiff layer for strength and shape and a fusable layer for ease of sealing. The melted polyethylene with embedded VPCI can also be die cast into arbitrary flexible shapes, typically several mm thick and up to 1 cm or more in lateral dimension.
The VPCI may be present in powder or tablets of substantially pure VPCI material. The VPCI is preferably mixed with or impregnated in a porous material, such as silica gel, or in void volume spaces of a porous continuous material, such as thin flexible sheets made from fibers or filaments. The VPCI may fill in the interstitial spaces of a porous sintered material, such as glass, metal or plastic, or may be dissolved or dispersed in granules of polymeric material. A VPCI package may contain a single component, a mixture of components, or a mixture of various carriers with different components.
The polymeric matrix for packaging the VPCI may be present in a simple sealed bag. The polymeric matrix also can be a sealed bag with one stiff surface carrying a pressure sensitive adhesive or a cylinder or a box made of thick molded polymer and thin polymer, and the emission rate of the VPCI is controlled by the type and thickness of the polymer matrix. The polymer matrix also can be a package made of a polymer with low permeability and another polymer with high permeability.
Although the disk drive is sealed in a housing, a breather filter is preferably used for equilibrating the pressure within the disk drive enclosure with the external pressure. The breather filter for use with VPCI should contain at least one diffusion barrier to minimize loss of VPCI from the drive environment. Many breather filters contain carbon or other adsorptive materials. In this case, a diffusion barrier should be present between the adsorptive material and the drive interior to minimize adsorption of the VPCI. A diffusion barrier is a high aspect ratio channel through which a vapor must diffuse to pass from the inlet to the exit. The typical diffusion barrier channel is 10 mm long and has a cross-sectional area of 0.4 mm2.
One type of corrosion takes place when adsorbed water and ions are present on the surfaces of the magnetoresistive or magnetic tunnel junction and inductive write head and the recording disk. The adsorbed water acts as an electrolyte, facilitating the migration of ions from regions of higher to lower electrochemical potential. One form of effective VPCI prevents the charge flow in the corrosion circuit, thereby eliminating the corrosion current.
The VPCI package also is held in an impermeable container punctured by one or more small pinholes for controlling the diffusion rate of the VPCI. In this embodiment, the delivery of the VPCI is metered by a diffusion channel, such as a small tube, or pinholes for controlling the diffusion rate of the VPCI.
It is therefore an object of the present invention to provide a hard disk drive having a VPCI package for preventing the corrosion of the metal films of GMR or MTJ and inductive write heads and magnetic recording disks with or without thin carbon overcoats, and other electrical interconnections of hard disk drives in normal or condensing humidity environments. Specifically, the VPCI package is advantageous for hard disk drives having self-burnishing sliders (so called self-limiting wear pad sliders) supporting GMR or MTJ and inductive write heads having no carbon overcoats.